1. Field of Invention
This invention relates to methods and systems for detecting erasures in a stream of symbols.
2. Description of Related Art
Generally, digital communication channels have the capacity to transport a stream of digital data at a determinable rate with the caveat that a number of symbols within the data stream will be corrupted. One primary reason behind this data corruption is that communication channels suffer from noise contamination. That is, as data is transported through a given communication channel, any resident noise within the communication channel will contaminate the data stream. As a result, any device receiving the corrupted data will have to compensate for symbol errors that will arise due to this noise contamination.
In order to address this problem, a number of error correction schemes have been devised to detect and correct corrupted symbols. For example, a number of block codes, such as the Reed-Solomon (RS) code and the more general Bose-Chadhuri-Hocquenghem (BCH) code, have been developed to detect and correct multiple symbol errors within a block of data. Yet, it is to be appreciated that there is a limit on the number of symbols that a given correction scheme can address for a given block of coded data, and that the performance of these detection/correction schemes suffers when used with large block lengths.
However, it is well known in the communication arts that if the positions of symbol errors are known a priori, then the error correction capacity of a given RS block of data can be doubled. While the locations of corrupted symbols within a block of data are generally unknown prior to decoding, in some cases it is nonetheless sometimes possible to determine the locations of symbol errors prior to decoding. When symbols are characterized by an unknown error value but a known error location, these symbols are referred to as “erasures”. When an erasure is detected, it is advantageous to mark the erasure's location in some manner so that a block decoding device can utilize the additional information in the decoding process.
While there are a number of known techniques used to detect symbol erasures, these techniques still often fail to appropriately mark symbols that can clearly be recognized as erasures. Furthermore, such techniques can also mischaracterize erasures as good data. Accordingly, new techniques to detect symbol erasures are desirable.